Polymers are used in a wide range of applications due to their stability, elasticity, light weight, strength, ease of fabrication and formulation, and low cost. In applications where flexibility, elasticity, and resilience are desired, amorphous polymers having glass transition temperatures (Tg) below use temperatures (typically about 25.degree. C. or below) are particularly useful. To achieve this, certain types of monomers are selected, often dienes such as isoprene and butadiene. These diene monomers are readily available at low cost and produce low Tg polymers. However, isoprene and 1,3-butadiene have relatively high vapor pressures at ambient temperatures (i.e., 20-25.degree. C.). In addition, 1,3-butadiene is tumorigenic, is explosive when mixed with air, and readily forms the undesired dimer 1-vinyl-4-cyclohexene when heated. These factors make the polymerization of these diene monomers challenging in large scale processes. Accordingly, it would be desirable to use diene monomers that are less volatile and more stable than isoprene or 1,3-butadiene that also produce low Tg polymers.
The flexibility, elasticity and resilience of polymers are useful in many applications, and comprise a variety of forms, including films, fibers, foams and bulk items such as tires. Of particular interest to the present invention are polymeric foams. In addition to containers and packaging, polymeric foams have been used as absorbents in absorbent articles such as diapers and catamenial products. See, for example, U.S. Pat. No. 4,029,100 (Karami), issued Jun. 14, 1977, that discloses a shape-retaining diaper that can employ a foam element in the crotch area of the absorbent pad assembly in order to provide high wet resilience. Certain types of polymeric foams have been used in these absorbent articles for the purpose of imbibing, wicking and/or retaining aqueous body fluids. See, for example, U.S. Pat. No. 3,563,243 (Lindquist), issued Feb. 6, 1971 (absorbent pad for diapers and the like where the primary absorbent is a hydrophilic polyurethane foam sheet); U.S. Pat. No. 4,554,297 (Dabi), issued Nov. 19, 1985 (body fluid absorbing cellular polymers that can be used in diapers or catamenial products); U.S. Pat. No. 4,740,520 (Garvey et al), issued Apr. 26, 1988 (absorbent composite structure such as diapers, feminine care products and the like that contain sponge absorbents made from certain types of super-wicking, crosslinked polyurethane foams).
The use of absorbent foams in absorbent articles such as diapers can be highly desirable. If made appropriately, open-celled hydrophilic polymeric foams can provide features of capillary fluid acquisition, transport and storage required for use in high performance absorbent cores. Absorbent articles containing such foams can possess desirable wet integrity, can provide suitable fit throughout the entire period the article is worn, and can minimize changes in shape during use (e.g., due to swelling, bunching). In addition, absorbent articles containing such foams can be easier to manufacture on a commercial scale. For example, absorbent diaper cores can simply be stamped out of continuous foam sheets and can have considerably greater integrity and uniformity than absorbent fibrous webs. Such foams can also be molded into any desired shape, or even formed into integral, unitary diapers.
Accordingly, it would be desirable to develop polymers that: (1) are flexible, elastic and resilient so as to be useful in making films, adhesives, elastics, and the like; (2) can be made using monomers that are less volatile than isoprene or butadiene; (3) provide low Tg polymers. It would be particularly desirable to be able to make absorbent foams from such polymers that: (a) have adequate or preferably superior absorbency characteristics, including capillary fluid transport capability, so as to be desirable in high performance absorbent cores used in absorbent articles such as diapers, adult incontinence pads or briefs, sanitary napkins and the like; (b) are sufficiently flexible and soft so as to provide a high degree of comfort to the wearer of the absorbent article; and (c) can be manufactured on a commercial scale, at relatively low cost.